Alternating-current motor.



E. P. W. ALEXANDERSON. ALTERNATING CURRENT MOTOR. APPLIOATIOI FILED MAY 19, 1906.

Patented May 4, 1909.

9%? I 59 {W g may 2 SHEETS-SHEET 1.

Patented May 4, 1909.

2 SHEETS-SHEET Z UNITED STATES PATENT onnrca.

ERNST l v W. ALEXANDERSON, OF SGHENIQGTAD-Y, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

ALTERNATING-C Specification of Application filed May 19,

nections for such motors so as to improve their commutation.

. My invention, in one aspect, relates specifically to multipola'r motors having wave-f wound armatures.

It has been proposed heretofore toemploy a plurality of armature windings connected to successive commutator segments and to use a brush of a width insufficient to bridge adjacent segments connected to the same winding, for the purpose of avoiding shortcircuits during commutation. With such an arrangement each winding is successively open-circuited, as the segmen ts to which it is connected pass from beneath a brush, but short-circuiting of individual coils upon themselves in commutation is avoided by this arrangement. In the case of a wavewound armature, however, if it is attempted to employ more than one brush or set of brushes of each polarity, internal short-circuits are produced, even with a plurality of windings and narrow brushes. This fact a pears from laying out such a winding. t will be seen, for instance with three windings, that starting from one brush on winding 1 and proceeding to a second brush, which connects winding l -2, passing through that brush to winding 2, thence to another brush and through that brush to winding 3, then to still another brush, a path will be found back to winding 1, so that a complete circuit around the armature is closed directly on itself. This short-circuit, which comprises as many coils as there are poles, is subjected during commutation to the entire alternating field of the motor, and consequently pro- 1 For duces excessive heating and sparking. this reason it has been customary heretofore to use only one brush or set of brushes of each polarity in \\'ave-wound alternating-;

current motors. 'It is frequently desirable, however, in order to reduce the size of com- URRENT MOTOR.

Letters Patent. Patented May 4, 1909.

1906. Serial N0. 317,764.

brushes of each polarity. One feature of my i invention consists in. a novel arrangement of 5 windings, whereby the use of the desired number of brushes is rendered possible. my invention, in one aspect, consists in arranging each of thewave-windings of the ar mature. with a pitch exactly equal. to unity, so that the number of commutator segments is exactly divisible by the number of poles and windings. Consequently, if a commutator segment is at the point of engaging one brush, other segments connected to the same winding will be at that instant engaging all the other brushes. The same windings are engaged by all the brushes-at the same time, and all of one winding is open-circuited when any portion of it is ope -circuited. With such an arrangement it will be found impossible to trace an internal shortcircuit, as is possible with the usual fractional pitch windlugs. For instance, if three windings are employed and a brush not wider than two segments is used, if one brush connecting windings 1 and 2, all the other brushes will similarly be connectingwindings l and 2,

cuited-so that no path can be found from winding 2 to winding 3, and thence back through another brush to winding 1.

When a number of brushes of each polarity are employed, it is of course necessary that these brushes should be connected together. If this connection is made directly, a difference in the voltages at the brushes of the same polarity may produce heavy cross-currents. 1t hasbcen proposed before to insert resistances or other impcdances between the brushes .of thesamc polarity, in order to avoid these cross-currents in alternating- .curront motors. One of the features of my invention consists in employing the usual compensating winding for this purpose by inserting portions of it in the connecuons between brushes-of the same polarity. Each portion of the compensating winding being in inductive relation to a corresponding portion of the armature winding oii'crs practically no impedance to current lion ing from an external source to the brushes, but offers a high impedance to a current firming from pone brusl'i through the compensating \uinding to another brush of the same polarity. In fact, the compensating winding acts like 3 a difi'ercntial choke-coil, maintaining a pracand winding 3 will be completely open-cir-.

llll

llli

lUi i mutator, to employ a plurality of sets of l tically uniform distributionpf the urrent- 1':

from the external source between the brushes.

My invention will best be understood by reterenceto the accompanying drawings, in which I Figure 1 shows diagrammatically in development a portion of the armature winding and connections of a motor arranged in accordance with my invention; Fig. 2 shows a diagrammatic view of one complete armature winding; and Fig. 3 shows 'diagrammat-' ically the connections of the motor.

In Fig. 1, a, a a and a represent four wave-windings which'are connected to suc ceesive. commutator segments. The positions of the magnetic field poles of the motor are indicated in dotted lines by F F, F and F It will be seen that each winding has a pitch exactly equal to unity,that is, to the distance between the center lines of the oles. Consequentl if two brushes 1; and are arranged symmetrically with respect to the poles F and F*,or in other words, diametrically op osite each other on the commutator, both rushes will be in symmetrical position with respect to all the windings. It will be seen that the brush-width is somewhat less than three commutator segments, so .that each brush in the position shown engages windings a, a and 0 while winding a is open-circuited at both brushes.

Since the pitch of'each armature winding is unity the number of commutator segments for each winding will be a number divisible by the number of oles, instead of being one or two greater or ess than a multiple of the ole number, as in the usual arrangement. bonsequently, a winding somewhat different from a standard winding is required for such a motor, and I have indicated in Fig. 2 one suitable arrangement of armature winding.

In this figure only one of the armature windings is shown. It will be understood that the other windings will be arranged in precisely the same manner. The armature winding a is shown carried in twenty slots, five per pole. Consequently, the pitch of the winding is five slots. Starting with the upper conductor in slot 1, it will be seen that the winding progresses successively to slots 6, 11 and 16; the pitch in each case being five slots. The lower conductor in slot 16 is connected to the upper conductor in slot 2; this end connection being somewhat longer than the other connections in order to avoid closing the winding directly upon itself after passing once around the armature. From slot 2 the Winding ro resses to slots 7, 12, 17, 3, 8, etc., until lnaily the lower conductor in slot 5 is reached. This conductor is simply connected to the upper conductor in slot 1 so as to close the Winding upon itself.'

This winding which I have shown is simply one suitable arrangement, and other forms ot winding which permit of using a number ceases of commutator segments divisible by the number of poles may be employed.

It will be seen in Fig. 1 that brushes l) and 6 are of the same polarity, and consequently should be connected together. Instead of connecting these brushes directly, the conncction from brush 0 to the external source is made through a portion 0 of the compensating winding of the motor, While the conncction from brush 0 is similarly made through a portion 0 of the compensating winding. Brushes b and 5" of the op osite polarity are shown in dotted lines in big. 1.

The complete connections of a series compensated motor arranged in accordance with my invention are shown in Fi These connections may be traced as f0 lows: Starting from the lower motor terminal the current passes through the field coils f f, f and f in series. Coming from coil f 4 the cur rent divides, part passing through compensating coil c to brush 1), and the remainder v assing through compensating coil c to rush After passing through the armature winding the current flows through brushes 5 and b passing from the former brush through compensating coil 0 to the upper motor terminal, and from the brush 5 through compensating coil 0 to the upper motor terminal.

Compensating coil 0 is in inductive relation to .the ortion ofthe armature winding with which lirush b is in engagement. Consequently practically no impedance is offered to current flowing from the external source through compensating coil 0 to t iis brush, but any current flowing from brush 6 to brush 6 must flow through the compensating coils c? and c in series, and these coils offer a high impedance to the flow of such a crosscurrent. In this manner a cross-flow of current between brushes of the same polarity is prevented without using auxiliary impedances of any kind, and at the same time better compensation is secured, since each portion of the armature winding is directly in series With the adjacent portion of the compensating Winding, so that if any inequalities in current-flow exist in the (litterent portions of the armature, due to difierences in the air-gap or other cause, the compensating winding for each portionof the armature nevertheless carries precisely the correct amount or" current for compensation.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In a multipolar alternating-current motor, an armature having a plurality of Wavewindings connected to successive commuta tor segments, each of said windings having a coil pitch exactly equal to the distance between poles, and a plurality of brushes of each polarity distributed symmetrically around the commutator.

2. in a multipolar alternating-current motor, an armature having a plurality of wave- 1 windings connected to successive commutat tor segments, each of said windings having a coil pitch exactly equal to the distance be- I tween poles, and a plurality of brushes of each polarity distributed symmetrically around the commutator the width. of each brush being insufficient to bridge adjacent commutatonsegmcnts connected to the same winding.

25. In a multipolar alternating-current motor, an armature having a commutator with a number of segments divisible by the number of poles of the motor, a plurality of wave windings. carried by the armature connected to successive commutator segments, and a plurality of brushes of each olarity distributed symmetrically around t 1e commutator.

1. In a multipolar alternating-current motor, an armature having a .:onnnutator with a number of segments divisible by the number of poles of the motor, a plurality of wave windings carried by the armature connected to successive commutator segments, and a plurality of brushes of each polarity distributed symmetrically around the commutator, the width of each brush being insidiieient to bridge adjacent segments connected to the same winding.

5. In a multipolar' alternating-current' motor, a hold Winding, a compensating winding, an armature having a plurality of wave windings connected to successive commutator segments, each of said windings having a coil-pitch exactly equal to the distance between the poles, a plurality of brushes of each polarity distributed around the commutator, and conductors connecting each brush individually directly in series with a portion of the compensating winding. 4

6. In a multipolar alternating-current motor, a field winding, a compensating Winding, an armature having a plurality of wave windings connected to successive commutator segments, each of said windings having a coil-pitch exactly equal to the distance between the poles, brushes distributa d around the commutator and corresponding innumber to the poles of the motor, and conductors connecting each brush directly in series with the compensating winding for the adjacent polo.

7. in a iiiultipolar alternating-current motor, a field winding, a compensating winding, an armature having a plurality of wave windings connected to successive commute tor segments, each of said windings hav. a cod-pitch exactly equal to the dist ecu the poles, a plurality of brusln oolarity distributed around the con or, and connections between brush). same polarity each including a portion compensating winding.

e, in a multipolar alternating-current motor, a field winding, a com ensating wind.- ing, an armature having a pliirality of wave windings connected to successive connnutator segments, each of said windings having a coil-pitch exactly equal to the distance between the poles, a plurality oi brushes or each polarity distributed around the com mutator, and connections from an external source of current to each brush, each connection including a portion of the compensating winding.

9, In a multipolar alternating-currcnt motor, a lield winding, a compensating wind ing, an armature having a plurality of wave windings connected to successive connnutator segments, each of said windings having a coil-pitch exactly equal to the distance be tween the poles, brushes distributed arourm the commutator and corresponding in number to the poles of the motor, and connections from an external source of current to each brush, each COIlllLCtlOll including the compensating winding for the pole adjacent to that brush.

In WltIlOSS whereof, l have hereunto set my hand this 18th day of May, 1906.

ERNST F. W ALEXANDEHSON 

